Carrier-aggregation-based handover method

ABSTRACT

Provided are a method for performing handover in a cellular mobile communication system that supports a carrier aggregation, and a user equipment and a node base (NodeB) using the method. A connection between the user equipment and the NodeB may be maintained and information may be exchanged using a plurality of serving carriers. Before performing the handover, the user equipment may perform measurement with respect to a neighboring NodeB supporting the carrier aggregation, and may provide parameter information to the NodeB in order to support a carrier aggregation function required for the handover. In a handover seamless environment, the continuity of a service may be provided and the performance of the service may be enhanced.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/695,168, filed on Jan. 8, 2013, which is a 371 U.S. patentapplication of PCT application No: PCT/KR2011/002919 filed Apr. 22,2011, which claims priority to, and the benefit of, Korean PatentApplication No. 10-2010-0039827, filed on Apr. 29, 2010, Korean PatentApplication No. 10-2010-0057550, filed on Jun. 17, 2010 and KoreanPatent Application No. 10-2010-0074890, filed on Aug. 3, 2010, in theKorean Intellectual Property Office (KIPO), the entire contents of whichare hereby incorporated by reference.

TECHNICAL FIELD

The following embodiments relate to a method for performing a handoverin a cellular mobile communication system supporting a carrieraggregation, and an apparatus using the method.

BACKGROUND ART

In a cellular mobile communication system, a handover method andprocedure enables a base node (NodeB) and a user equipment to maintainconnection using a single serving carrier and to exchange information.The handover method and procedure may be performed by a procedure thatis basically based on connection using the single serving carrier.

A source or serving NodeB providing a service to user equipments maydetermine a handover with respect to a user equipment that is positionedin a handover region or a handover environment, and may determine atarget NodeB based on a measurement result reported by the userequipment, and request the target NodeB for the handover.

A handover request message may include connection information, forexample, a Radio Access Bearer (RAB) context that is established withthe user equipment.

The target NodeB may review whether it is possible to receive thecorresponding user equipment according to a handover request from thesource NodeB. When it is possible to receive the corresponding userequipment, the target NodeB may transmit a response message with respectto the handover request.

A handover response message may include a scheduling identifier, thatis, a Cell-Radio Network Temporary Identifier (C-RNTI) of the targetNodeB for the user equipment to be handed over, radio resourceinformation for a random access, and the like.

The user equipment may receive information associated with the targetNodeB together with a handover execution command via the source NodeB.The user equipment having received the information may access the targetNodeB. When the connection with the target NodeB succeeds, the userequipment may transmit a handover complete message.

The aforementioned handover method may be suitable for a system that mayprovide a service using a single serving carrier between the NodeB andthe user equipment.

For a NodeB and a user equipment that supports a carrier aggregationusing a plurality of carriers, there is a need to introduce anadditional operation and control procedure with respect to a sourceNodeB, a target NodeB, and a user equipment.

Disclosure of Invention Technical Goals

An aspect of the present invention provides a handover method that maydecrease a handover delay in a carrier aggregation environment andmaintain a service continuity, and a user equipment and a NodeB usingthe handover method.

Technical Solutions

According to an aspect of the present invention, there is provided ahandover providing method of a source node base (NodeB) and a targetNodeB, the method including: receiving, by the source NodeB from a userequipment, a measurement result with respect to component carriers of aneighboring NodeB or the source NodeB; determining, by the source NodeB,the target NodeB; transmitting, by the source NodeB, a handover requestmessage to the target NodeB; transferring, by the target NodeB, ahandover request acknowledgement (ACK) message to the source NodeB; andtransmitting, by the source NodeB to the user equipment, a handoverexecution command including a handover parameter.

The handover providing method of the source NodeB and the target NodeBmay further include determining, by the target NodeB, component carrierconfiguration information. The target NodeB may transfer the componentcarrier configuration information to the source NodeB using the handoverrequest ACK message, and the handover parameter may include thecomponent carrier configuration information.

The component carrier configuration information may correspond to one ofsingle component carrier information, primary component carrierconfiguration information, and the primary component carrierconfiguration information and secondary component carrier configurationinformation.

The handover request message may include a measurement result withrespect to component carriers of the target NodeB.

The handover providing method of the source NodeB and the target NodeBmay further include determining, by the target NodeB, an uplink accesscomponent carrier. The target NodeB may transfer uplink access componentcarrier information to the source NodeB using the handover request ACKmessage, and the handover parameter include the uplink access componentcarrier information.

The handover providing method of the source NodeB and the target NodeBmay further include: determining, by the target NodeB, component carrierconfiguration information of a primary component carrier and a secondarycomponent carrier; and transmitting a component carrier configurationand activation control message to the user equipment.

The component carrier configuration information may include both of adownlink component carrier and an uplink component carrier, or mayinclude only one information.

According to another aspect of the present invention, there is provideda handover method of a user equipment, including: transmitting, to asource node base (NodeB), a measurement result with respect to componentcarriers of a neighboring NodeB, a target NodeB, or the source NodeB;receiving, from the source NodeB, a handover execution command includinga handover parameter; attempting an access to the target NodeB and anuplink synchronization establishment; receiving, from the target NodeB,a response with respect to a resource assignment for an uplink accessattempt and a synchronization establishment complete; and transmitting ahandover complete report message to the target NodeB.

The handover parameter may include component carrier configurationinformation.

The handover method of the user equipment may further include:attempting the access to the target NodeB and the uplink synchronizationestablishment; receiving, from the target NodeB, the response withrespect to the resource assignment for the uplink access attempt and thesynchronization establishment complete; and transmitting the handovercomplete report message to the target NodeB.

The handover parameter may include uplink access component carrierinformation.

The handover method of the user equipment may further include:attempting the access to the target NodeB and the uplink synchronizationestablishment using a component carrier based on the uplink accesscomponent carrier information; completing a response to the access andthe uplink synchronization establishment; reporting to the target NodeBabout the measurement result with respect to the component carriers ofthe target NodeB using an uplink radio resource allowed by the targetNodeB; and receiving a component carrier configuration and activationcontrol message from the target NodeB.

According to still another aspect of the present invention, there isprovided a method of changing a component, the method including: settinga user equipment to measure a mobility management; receiving ameasurement result obtained by measuring a radio channel quality withrespect to component carriers; determining a handover procedure forchanging of a primary component carrier based on the measurement resultand a load status of each of the component carriers, and performing arelevant control procedure; transmitting, to a user equipment,information associated with a component carrier to be configured as anew primary component carrier, and commanding a handover execution forchanging of the primary component carrier; and exchanging controlinformation with the user equipment using the new primary componentcarrier.

The component changing method may further include: transmitting, to theuser equipment, new primary component carrier information and randomaccess resource assignment information; receiving a random accesspreamble from the user equipment using the new primary componentcarrier; and transmitting random access response information to the userequipment using the new primary component carrier.

The handover execution command may include timing advance referenceprimary component carrier configuration information and pathlossreference primary component carrier configuration information for uplinktransmit power setup.

The component changing method may further include transmitting acomponent carrier configuration message to the user equipment.

The component carrier configuration message may include at least one ofa primary component carrier index, control information for management ofthe primary component carrier, at least one secondary component carrierindex, and control information for management of a secondary componentcarrier.

According to yet another aspect of the present invention, there isprovided a method of changing a component, the method including:measuring a mobility management based on a configuration from a servingnode base (NodeB); transmitting, to the serving NodeB, a measurementresult obtained by measuring a radio channel quality with respect tocomponent carriers; receiving, from the serving NodeB, informationassociated with a component carrier to be configured as a new primarycomponent carrier; and exchanging control information with the servingNodeB using the new primary component carrier.

The component changing method may further include: receiving, from theserving NodeB, new primary component carrier information and randomaccess resource assignment information; transmitting a random accesspreamble to the serving NodeB using the new primary component carrier;and receiving random access response information from the serving NodeBusing the new primary component carrier.

The component changing method may further include transmitting, to theserving NodeB, a control message indicating a primary component carrierchange complete and a secondary component carrier configurationcomplete.

Effect of the Invention

According to embodiments of the present invention, there may be provideda handover method that may decrease a handover delay in a carrieraggregation environment and maintain a service continuity, and a userequipment and a node base (NodeB) using the handover method.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a handover in a carrier aggregationenvironment according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating a message transmission procedure thatis configurable using a handover method according to an embodiment ofthe present invention;

FIG. 3 is a diagram illustrating a message transmission procedure thatis configurable using a handover method according to another embodimentof the present invention;

FIG. 4 is a diagram illustrating a procedure for performing handover forcomponent change according to an embodiment of the present invention;

FIG. 5 is a diagram illustrating a procedure for performing handover forcomponent change according to another embodiment of the presentinvention; and

FIG. 6 is a diagram illustrating a configuration of a component carrierconfiguration or re-configuration message according to an embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

FIG. 1 is a diagram illustrating a handover in a carrier aggregation(CA) environment according to an embodiment of the present invention.

Each of a source node base (NodeB) 110 and a target NodeB 120corresponds to a NodeB to support carrier aggregation (CA), and mayinclude a plurality of component carriers (CCs). Here, each of the CCsmay operate as a single cell within the same NodeB.

Referring to FIG. 1, CCs of the source NodeB 110 may correspond toconfigured CCs 140. CCs of the target NodeB 120 may correspond tomeasured CCs before handover (HO) 150.

The source NodeB 110 may support a CA function by including a pluralityof component carriers. The plurality of component carriers of the sourceNodeB 110 may include CC#1 142 of a frequency f1, CC#2 144 of afrequency f2, CC#3 146 of a frequency f3, and CC#4 148 of a frequencyf4.

The target NodeB 120 may support a CA function by including a pluralityof component carriers. The plurality of component carriers of the targetNodeB 120 may include CC#1 152 of the frequency f3, CC#2 154 of thefrequency f4, CC#3 156 of a frequency f5, and CC#4 158 of a frequencyf6.

Here, each of the frequencies f1, f2, f3, f4, f5, and f6 may denote a CCof a different center frequency.

Accordingly, the frequencies f3 and f4 may configure CCs of both thesource NodeB 110 and the target NodeB 120 as the same frequencycarriers. The frequencies f1 and f2 of the source NodeB 110, and thefrequencies 13 and f4 of the target NodeB 120 may configure CCs of thesource NodeB 110 and the target NodeB 120 as different frequencies.

A user equipment (UE) 130 may belong to the source NodeB 110, and maymaintain a connection, for example, Radio Resource Control (RRC)connection, with the source NodeB 110 and may exchange information.

All of the CCs 142 through 148 constituting the source NodeB 110 may beconfigured in the UE 130.

The UE 130 may control a portion of or all of the configured CCs 140 tobe activated or deactivated based on an amount of data to be exchanged,a load status of the NodeB 110, and a load status of each of the CCs142, 144, 146, and 148 of the NodeB 110.

The UE 130 may configure, as a primary component carrier (PCC), one ofactivated CCs configured for control signaling exchange, and mayconfigure remaining CCs as secondary component carriers (SCCs).

The source NodeB 110 and the UE 130 enable control signaling, Radio LinkFailure (RLF), resource assignment for a random access procedure, andthe like to be performed via the PCC.

In the case of supporting a CA function using a plurality of carriers, athreshold for measurement of a separate radio channel quality may be setfor PCC change and SCC change between CCs configured or activated in thepredetermined UE 130. Here, the SCC change may include addition ordeletion of the SCC.

Accordingly, the source NodeB 110 may set and control the UE(s) 130 toperform measurement with respect to each of the configured CCs 140within the source NodeB 110, and to report the measurement result.

When a radio channel quality measurement result, for example, a channelquality indicator (CQI) of each of the CCs 140 measured and reported bythe UE(s) 130 satisfies a threshold criterion used or required for thePCC or SCC change, the source NodeB 110 may control configuration of thePCC or the SCC to be changed for each UE 130 using a control message.

Also, in order to support a UE mobility function, the source NodeB 110may set and control the UE 130 to measure and report CCs of neighboringNodeBs having the same frequency or a different frequency in addition tothe CCs 142, 144, 146, and 148 of the source NodeB 110.

When the UE 130 is determined to be present in a handover region due toa deteriorated channel quality of a CC 142, 144, 146, or 148 of thesource NodeB 110 based on the measurement result of the UE 130, or whena channel quality of a CC(s) of a neighboring NodeB satisfies athreshold criterion set for handover based on the channel qualitymeasurement result of CC(s) of the source NodeB 110 and the target NodeB120, the source NodeB 110 may determine the handover is to be performed.

When the source NodeB 110 determines the handover is to be performedbased on the result measured and reported by the UE 130, the sourceNodeB 110 may determine the target NodeB 120 based on the measurementresult.

In this example, a target NodeB determination may indicate that a singleCC 152, 154, 156, or 158 is selected from the CCs 150 of the targetNodeB 120.

The source NodeB 110 may request the target NodeB 120 for handover withrespect to the corresponding UE 130. In this instance, the source NodeB110 may provide a radio channel quality measurement result associatedwith the CCs 152 through 158 of the target NodeB 120 measured andreported by the UE 130, in addition to a capability of the correspondingUE 130, RAB information, and the like.

The radio channel quality measurement result transmitted from the sourceNodeB 110 to the target NodeB 130 may include information that isprovided to help the target NodeB 120 to configure a CC for thecorresponding UE 130.

Radio channel quality measurement information associated with the CC(s)may be expressed in a form of a signal to interference ratio (SIR), asignal to interference plus noise ratio (SINR), a reference signalreceived power (RSRP), a reference signal received quality (RSRQ), areceived signal strength indicator (RSSI), and the like.

Using the radio channel quality measurement result measured and reportedby the UE 130, the source NodeB 110 may provide CC configuration listinformation including at least one CC that may be configurable as a PCCand/or an SCC by the target NodeB 130.

The target NodeB 120 receiving a handover request from the source NodeB110 may determine a PCC and an SCC(s) in the target NodeB 120 for thecorresponding UE 130 based on UE information, the measurement resultwith respect to the CCs 150 of the target NodeB 130 or CC configurationlist information, and a load status including control signaling withrespect to each of the CCs 152, 154, 156, and 158 of the target NodeB120.

The target NodeB 130 may transmit, to the source NodeB 110, informationused for the handover and configuration information associated with thePCC and the SCCs, using a response message with respect to the handoverrequest.

Information used for the handover may include the following parameters:

1) Scheduling identifier, for example, a C-RNTI in the target NodeB 120

2) Information for encoding, for example, security key information

3) CC configuration information, for example, single CC information, PCCconfiguration information, at least one SCC configuration information

4) Radio resource information for random access (RA) to the target NodeB120, for example, an RA CC, an RA radio resource position, RA preambleindex information, and the like.

A method different from the aforementioned method may be applied. Forexample, only PCC configuration information in CC configurationinformation of the target NodeB 120 may be notified to the source NodeB110 using a handover request response message before the handover isperformed by the UE 130. After the UE 130 completes connection with thetarget NodeB 120, the target NodeB 120 may configure the SCC bytransmitting SCC configuration information using a separate controlmessage. Accordingly, in this case, the target NodeB 120 may transfer,to the source NodeB 110, only configuration information associated witha single CC 152, 154, 156, or 158.

Specifically, regardless of whether the source NodeB 110 provides radiochannel quality information associated with the CC(s) 150 of the targetNodeB 120 or configurable CC list information, the target NodeB 120 maytransmit, using a handover control message, PCC configurationinformation that is notified to the UE 130 to be handed over using thesource NodeB 110.

After the UE 130 to be handed over attempts an access to the PCC of thetarget NodeB 120 that is transferred via the source NodeB 110, thetarget NodeB 120 may configure SCCs.

The source NodeB 110 having received, from the target NodeB 120, aresponse message with respect to the handover request may transmit, tothe UE 130, a control message commanding the handover. The source NodeB110 may notify the UE 130 about parameter information used for thehandover that is transferred from the target NodeB 120.

The UE 130 having received the handover execution command from thesource NodeB 110 may attempt an access to the target NodeB 120 based onthe transferred handover parameter information. The UE 130 may completeconnection establishment with the target NodeB 120 and transmit amessage indicating that the handover is successfully completed.

In a CC of the target NodeB 130 for which the UE 130 may perform RA inorder to attempt the access to the target NodeB 120, the followingmethods may be employed based on information transferred via the sourceNodeB 110:

1) Method of receiving information indicating a RA CC and access thetarget NodeB 120

2) Method of accessing a radio resource of a corresponding uplink (UL)CC using downlink (DL) CC and UL CC linkage information included insystem information of the target NodeB 120 when single CC information istransferred and the CC information indicates only DL CC

3) Method of verifying an UL PCC and attempting an access using PCCconfiguration information set and transferred by the target NodeB 120

After connection with the UE to perform the handover is set up, thetarget NodeB 120 may perform an SCC activation procedure by transmittinga control message for activating SCCs based on PCC and SCC configurationinformation that the target NodeB 120 has notified to the UE 130 via thesource NodeB 110.

When the target NodeB 120 does not transfer SCC configurationinformation to before the handover, the target NodeB 120 may perform anSCC configuration and activation procedure after the connection is setup between the target NodeB 120 and the UE 130

For the above SCC activation procedure, the target NodeB 120 may use aCC measurement result additionally received from the UE 130, and maytransmit separate control information to perform additional measurement.

FIG. 2 is a diagram illustrating a message transmission procedure thatmay be configurable using a handover method according to an embodimentof the present invention.

In operation 210, a UE 130 and a source NodeB 110 may communicate witheach other.

In operation 220, the source NodeB 110 may set the UE 130 to measure aCC by including a neighboring NodeB.

If necessary, the source NodeB 110 may set up a measurement gap.

In operation 225, the UE 130 may measure CCs of the neighboring NodeB,for example, the source NodeB 110 or a target NodeB 120, and may reportto the source NodeB 110 about a measurement result.

In operation 230, when a handover is determined to be required, thesource NodeB 110 may determine the target NodeB 130.

In operation 240, the source NodeB 110 may transmit a handover requestmessage to the target NodeB 120.

The source NodeB 110 may include, in the handover request message, themeasurement result with respect to the CC(s) of the target NodeB 120 andthereby transfer the handover request message to the target NodeB 120.

In operation 245, the target NodeB 130 may determine CC configurationinformation as one of the following 1) through 3):

1) Information associated with a single CC

2) PCC configuration information

3) PCC configuration information and information associated with atleast one SCC configuration

In operation 250, the target NodeB 120 may transfer CC configurationinformation such as CC configuration information of PCC or SCC(s) to thesource NodeB 110 using a handover request acknowledgement (ACK) message.

In operation 260, the source NodeB 110 may transmit a handover executioncommand to the UE 130.

The source NodeB 110 may include, in the handover execution command, ahandover parameter such as CC configuration information and the like,and thereby transmit the handover execution command to the UE 130.

In operation 270, the UE 130 receiving the handover command may attemptan access to the target NodeB 120 and UL synchronization establishment.

In operation 275, the target NodeB 120 may respond a resource assignmentwith respect to UL access attempt and a synchronization establishmentcomplete.

In the above response, the target NodeB 120 may also transmit anactivation control message with respect to CC(s) configured by thetarget NodeB 120.

Also, the target NodeB 120 may separately transmit the activationcontrol message with respect to the CC(s) configured by the target NodeB120.

In operation 280, the UE 130 may transmit a handover complete reportmessage to the target NodeB 120.

Regardless of that the target NodeB 120 makes a request or does not makea request in operation 275, the UE 130 may additionally report ameasurement result with respect to a CC of the target NodeB 120.

A measurement result message may allow an UL radio resource that may beassignable or available by the target NodeB 120 in operation 275.

In this case, before or after transmitting the handover complete reportmessage of operation 280, the UE 130 may transmit the measurement resultwith respect to the configured CC(s) together with the handover completereport message using the UL radio resource allowed by the target NodeB120. The UE 130 may transmit an activation message with respect to theCCs configured by the target NodeB 120 after receiving the additionalmeasurement result, instead of transmitting the activation message inoperation 275.

FIG. 3 is a diagram illustrating a message transmission procedure thatmay be configurable using a handover method according to anotherembodiment of the present invention.

Even though the handover method of FIG. 3 is similar to the handovermethod described above with reference to FIG. 2, configuration withrespect to CCs of the target NodeB 120 may be determined after handover.Accordingly, an example of the message transmission procedure that maybe configurable to be different from the message transmission procedureof FIG. 2 will be described.

Operations 310, 320, 325, 330, 340, 345, 350, 360, 370, 375, and 380 ofFIG. 3 may correspond to operations 210, 220, 225, 230, 240, 245, 250,260, 270, 275, and 280 of FIG. 2, respectively. Accordingly, furtherdetailed description related thereto will be omitted here and adifference between corresponding operations will be described.

Unlink the target NodeB 120 determines CC configuration information inresponse to the handover request of the source NodeB 110 of operation240 of FIG. 2 in operation 245, the target NodeB 120 may determine onlya CC required when the UE 130 sets up connection with the target NodeB120 in response to the handover request of the source NodeB 110 ofoperation 340 of FIG. 3 in operation 345.

In operation 350, the target NodeB 120 may transfer, to the source NodeB110, UL access CC information according to the above determination usinga handover request ACK message.

In operation 360, the source NodeB 110 may transmit a handover executioncommand to the UE 130.

The source NodeB 110 may include, in the handover execution command, ahandover parameter such as UL access CC information and the like andthereby, transmit the handover execution command to the UE 130.

In operation 370, the UE 130 receiving the handover command may attempta UL synchronization establishment and an access to the target NodeB 120using a corresponding CC based on the UL access CC information.

In operation 375, a response to the access and the UL synchronizationestablishment may be completed.

In operation 380, together with a handover complete report message, orafter transmitting the handover complete report message, the UE 130 mayreport to the target NodeB 120 about a measurement result with respectto CC(s) of the target NodeB 120 using the UL radio resource allowed bythe target NodeB 120.

In operation 385, the target NodeB 120 receiving the measurement resultmay determine CC configuration information of PCC and SCC(s), and thelike.

In operation 390, the target NodeB 120 may transmit, to the UE 130, a CCconfiguration control message and activation control message. Here, theCC may include the PCC and the SCC.

The target NodeB 120 may separately configure a CC configuration controlmessage and an activation control message and thereby, may transmit eachthereof to the UE 130 using a separate radio resource.

In the above description, the CC configuration procedure and theactivation procedure may be controlled using a separate control message.

For example, the CC configuration procedure may use an RRC controlmessage and the activation procedure may use a Media Access Control(MAC) control message.

However, when the separate activation procedure or the MAC controlmessage for activation is absent, the target NodeB 120 may assign aresource based on scheduling information with respect to CCs that areconfigured using the CC configuration procedure, and may transmitinformation. The UE 130 may also be controlled to receive DL informationtransmitted from the target NodeB 120 by monitoring schedulinginformation, and to transmit information using UL assignment informationassigned by the target NodeB 120.

For the above operation, the target NodeB 120 may control the UE 130 tomeasure and report a DL channel with respect to the configured CCs, andmay determine whether scheduling with respect to the configured CCs isavailable using a corresponding measurement result.

As described above, CC configuration information transferred by thetarget NodeB 120 via the source NodeB 110 may configure only DL CCs, ormay express both DL CCs and UL CCs. When configuring only the DL CCs, ULCCs corresponding to respective DL CCs may be acquired using systeminformation of the target NodeB 120, or may be acquired using a separatecontrol message.

Here, the measurement result with respect to CCs measured and reportedby the UE 130 may indicate only measurement information associated withthe DL CCs.

A method of applying a handover procedure may be employed for PCC changebetween CCs within a NodeB supporting a CA, instead of supportinghandover between NodeBs.

In a cellular mobile communication system based on an orthogonalfrequency division multiple access (OFDMA) system, synchronizationestablishment and maintenance of UL physical layer may be required tosecure the orthogonality between UEs in UL.

However, in the case of supporting a CA function using a plurality ofCCs, the one timing advance (TA) information may be applied alike to theplurality of CCs based on distance between center frequencies of CCs.

Specifically, when the distance, that is, a difference between thecenter frequencies is not great, the source NodeB 110 or the targetNodeB 120 may generate TA information for UL synchronizationestablishment based on a single CC, for example, a PCC among a pluralityof CCs configured in the UE 130, and may notify the UE 130 about thegenerated TA information. In this case, even though a transmission timein all the configured and activated CCs is updated and transmitted usingcorresponding TA information, the UE 130 may maintain the orthogonalitybetween UEs 130 in the UL.

Accordingly, when using the above property, a RA procedure required forUL synchronization establishment may not be required for handoverbetween CCs within the NodeB 110 or 120 changing PCC within the NodeB110 or 120.

However, for consistency in a system and TA for accurate ULsynchronization establishment between the NodeB 110 or 120 and the UE130, a process of configuring a reference CC may be required.

Also, when the UE 130 sets a transmission power used for transmission tothe NodeB 110 or 120, a process of configuring the reference CC may berequired in order to set the transmission power based on a pathlossbetween the NodeB 110 or 120 and the UE 130, or a radio channelenvironment.

For example, when the PCC or a primary cell is changed, the pathloss orthe radio channel environment may vary due to a change in a DL CC.Accordingly, a pathloss reference CC used to determine the transmissionpower in UL transmission may also be changed.

Accordingly, the NodeB 110 or 120 may notify the UE 130 aboutinformation associated with the changed reference CC, or may control theUE 130 to configure the pathloss reference CC based on mappinginformation of an UL and a DL recognized by the UE 130 using the systeminformation.

FIG. 4 is a diagram illustrating a procedure for performing handover forcomponent change according to an embodiment of the present invention.

In the present procedure, handover for component change in a servingNodeB 410 may be performed without a RA procedure.

In operation 410, a UE 130 and the serving NodeB 410 may communicatewith each other.

In operation 420, the serving NodeB 410 may set the UE 130 to measure amobility management.

In operation 430, the UE 130 may measure a radio channel quality withrespect to all the CCs of the serving NodeB 410 as well as CCs that areconfigured according to setup of the serving NodeB 410, and may report ameasurement result.

In operation 440, the serving NodeB 410 may determine a handoverprocedure for PCC change, that is, PCC change between CCs within a NodeBbased on a load status of each CC and the measurement result reported bythe UE 130, and may perform a relevant control procedure.

In operation 450, the serving NodeB 410 may transmit, to the UE 130,information associated with a CC to be configured as a new PCC, and maycommand the handover for the PCC change within the serving NodeB 410.

The serving NodeB 410 may transmit TA reference PCC and pathlossreference PCC configuration information for UL transmission power setuptogether with the handover execution command.

In operation 480, the serving NodeB 410 and the UE 130 may exchangecontrol information via the PCC.

The serving NodeB 410 may notify the UE 130 about configurationinformation associated with a control channel of a UL PCC, for example,a physical uplink control channel (PUCCH).

Also, if necessary, the serving NodeB 410 may change a schedulingidentifier, for example, C_RNTI. In this case, the serving NodeB 410 maynotify the UE 130 about the scheduling identifier by also changing arelative scheduling identifier according to a use purpose, for example,a semi-persistent scheduling identifier and the like.

The serving NodeB 410 and the UE 130 may also change a reference CC forUL synchronization establishment using a new PCC.

The serving NodeB 410 may transmit the aforementioned pathloss referencePCC configuration information for UL transmission power setup to the UE130 together with setup information associated with a control channel ofUL PCC. Also, the UE 130 may transmit, to the serving NodeB 410, acontrol message indicating a PCC change complete and/or an SCCconfiguration complete.

As described above, when a handover procedure for changing a PCC withinthe serving NodeB 410 is performed without performing a RA procedure, aTA reference CC for an UL physical layer synchronization establishmentmay be configured as a predetermined configured and activated CC withoutbeing limited to the PCC. Accordingly, in operation 480, an existingconfigured CC may be continuously applied without changing the referenceCC with the new PCC.

As shown in FIG. 4, when the PCC is changed by omitting the RA procedurefor an initial access to a target serving cell or UL physical layersynchronization configuration in the general handover procedure, amethod of assigning and applying a predetermined RA preamble resourcemay be employed to apply an existing control message.

In this instance, when the serving NodeB 410 includes, in the handoverexecution command for PCC change, index information of a predeterminedRA preamble, for example, a preamble having all the values as ‘0’ or ‘1’in operation 450, the UE 130 may recognize the PCC change procedure inwhich the RA procedure for an initial access to a new PCC serving cellis not performed.

As shown in FIG. 4, when the PCC change is performed without a generalRA procedure, the new PCC and the UE 130 may employ the followingmethods 1) through 4) to initiate the access:

1) Method in which the UE 130 is assigned with an UL radio resource bytransmitting scheduling resource information to the new PCC using ascheduling request of UL control channel information that is set for anew PCC serving cell in operation 450.

2) Method in which the serving NodeB 410 notifies the UE 130 about ULradio resource assignment information associated with the new PCCserving cell and the UE 130 transmits control information or trafficinformation required for UL using corresponding information in operation450.

3) Method in which the new PCC serving cell transmits UL or DL resourceassignment information to the corresponding UE 130 whereby the UE 130initiates transmission and reception with the new PCC serving cell afteroperations 450 and 480.

4) Method in which the serving NodeB 410 verifies CQI using an assignedradio resource in order to report CQI in UL control channel informationset for the new PCC serving cell and transmits UL or DL resourceassignment information to the corresponding UE 130, whereby the UE 130initiates transmission and reception with the new PCC serving cell inoperation 450.

FIG. 5 is a diagram illustrating a procedure for performing handover forcomponent change according to another embodiment of the presentinvention.

The handover for the component change in a serving NodeB 410 may beperformed through a RA procedure.

Operations 510, 520, 530, 540, 550, and 580 of FIG. 5 may correspond tooperations 410, 420, 430, 440, 450, and 480 of FIG. 4, respectively.Accordingly, further detailed description related thereto will beomitted here and only a difference between operations will be described.

In operation 550, the serving NodeB 410 may transmit new UL PCCinformation, RA resource assignment information, for example, RA radioresource position information, an RA preamble index, and the like, andmay command a handover execution for the PCC change in the serving NodeB410.

In this instance, the serving NodeB 410 may transmit TA reference PCCand pathloss reference PCC configuration information for UL transmissionpower setup together with the handover execution command.

In operation 560, the UE 130 may transmit a RA preamble using a new ULPCC.

In operation 570, the serving NodeB 410 may transmit RA responseinformation using a new DL PCC. In this instance, the serving NodeB 410may change a reference CC for TA and may assign a new schedulingidentifier.

In operation 580, the serving NodeB 410 may transmit control channelsetup information of the new UL PCC to the UE 130 and exchange controlinformation via the new PCC.

In this instance, the UE 130 may transmit, to the serving NodeB 410, acontrol message indicating a PCC change complete and/or an SCCconfiguration complete.

In the aforementioned PCC change procedure within the same NodeB, theserving NodeB 410 may transmit only DL PCC information in CCinformation, or may also transmit UL PCC information in operations 450and 550.

When the serving NodeB 410 transmits only DL PCC information, the UE 130may recognize mapping relationship between corresponding UL PCC or DL CCand UL CC based on acquired system information. Also, the serving NodeB410 may set the mapping relationship between the UL PCC or the DL CC andthe UL CC using a spate control message.

In addition, in the PCC change procedure within the same serving NodeB410, the serving NodeB 410 may change a PCC and modify SCC configurationusing a CC configuration or reconfiguration message. Specifically, inoperations 450 and 550, the serving NodeB 410 may control the UE 130 toperform the PCC change and the SCC reconfiguration by transmitting a CCconfiguration or reconfiguration message to the UE 130.

The CC configuration or reconfiguration message may include informationof the following 1) through 4):

1) PCC index

2) Control information for PCC management

3) At least one SCC index

4) Control information for SCC management

Each CC may be classified by defining a CC identifier within the servingNodeB 410. A PCC index in the CC configuration message may indicate a CCidentifier selected as a PCC.

The control information for the PCC management may correspond to controlinformation required to configure and maintain the PCC. The controlinformation for the PCC management may include a measurement referencevalue, for example, an Smeasure value, assignment information of aphysical layer resource, for example, UL or DL control informationtransmission resource, and the like, that maps PCC, CC configurationvalid reference information, for example, CC configuration start point,valid interval, and the like, DRX setup information, and the like.

The SCC index indicates an identifier of CC(s) configured as the SCClike the PCC index.

The control information for the SCC management may correspond to controlinformation required to configure and maintain the SCC. The controlinformation for the SCC management may include a measurement referencevalue, for example, an Smeasure value, assignment information of aphysical layer resource, for example, UL or DL control informationtransmission resource, and the like, that maps CC, CC configurationvalid reference information, for example, CC configuration start point,a valid interval, and the like, DRX setup information, and the like. TheDRX setup information may be set to be different for each CC and therebybe transmitted.

Also, the CC configuration message may be transmitted so that PCC or SCCconfiguration may be performed based on a listed CC index order withoutclassifying the PCC index, the SCC index, and the like. That is, a firstor a last CC index may be recognized as a PCC configuration indexwithout separate configuration information.

FIG. 6 is a diagram illustrating a configuration of a CC configurationor re-configuration message according to an embodiment of the presentinvention.

FIG. 6 illustrates four types of CC configuration messages 610, 620,630, and 640.

The first type CC configuration message 610 may include a PCC index 611,PCC management information 612, a number of SCCs 613, at least one SCCindex 614, and SCC management information 615.

The second type CC configuration message 620 may include a number of CCs621, a PCC index 622, PCC management information 623, at least one SCCindex 624, and SCC management information 625.

The third type CC configuration message 630 may include a number of CCs631, at least one CC index 632, PCC management information 633, and SCCmanagement information 624.

The fourth type CC configuration message 640 may include a number of CCs641, at least one CC index 642, and CC management information 643.

The aforementioned NodeB 110, 120, or 410 may be replaced with anothernode, for example, a relay, a small NodeB, a home NodeB, and the likeconstituting a mobile communication network that supports a CA using aplurality of CCs.

Also, in the aforementioned description, a CC may indicate atransmission frequency constituting a NodeB or a cell. Accordingly, aPCC may be defined as a primary cell and an SCC may be defined as asecondary cell.

The above-described exemplary embodiments of the present invention maybe recorded in computer-readable media including program instructions toimplement various operations embodied by a computer. The media may alsoinclude, alone or in combination with the program instructions, datafiles, data structures, and the like. Examples of computer-readablemedia include magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD ROM disks and DVDs;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and perform program instructions, suchas read-only memory (ROM), random access memory (RAM), flash memory, andthe like. Examples of program instructions include both machine code,such as produced by a compiler, and files containing higher level codethat may be executed by the computer using an interpreter. The describedhardware devices may be configured to act as one or more softwaremodules in order to perform the operations of the above-describedexemplary embodiments of the present invention, or vice versa.

Although a few embodiments of the present invention have been shown anddescribed, the present invention is not limited to the describedembodiments. Instead, it would be appreciated by those skilled in theart that changes may be made to these embodiments without departing fromthe principles and spirit of the invention, the scope of which isdefined by the claims and their equivalents.

1. A handover method performed by a target base station, the handovermethod comprising: receiving a radio channel quality information withrespect to component carrier related to neighboring cell from a sourcestation transmitting a setting information for carrier aggregation tothe source station, wherein the component carrier receives the settinginformation for carrier aggregation, and performing a handover procedurewith the target station using the setting information.